Retrievable blanking plug

ABSTRACT

Combination wireline fishing tool and retrievable blanking plug for use in conjunction with a seating nipple. The blanking plug has a fishing neck which extends from a shoulder located thereon. The fishing neck includes spaced overshot engaging members so that a fishing tool in the form of an overshot can be forced into engagement with either of the members. An axial counterbore extending into the blanking plug has a combination stop means and pressure relief means located therein, in the form of spaced breakable plugs. The counterbore further includes means for releasing the blanking plug from the seating nipple. Attached to the overshot in axially aligned relationship therewith is a probe arranged whereby part of the overshot must be positioned in attached relationship between the two spaced members in order for the probe to break a relief plug and equalize the pressure across the blanking plug. Part of the overshot must next be moved into a position between the shoulder and the lowermost overshot engaging member and the second breakable plug broken by the probe in order for the release device to be actuated.

nited States Patent Vann May 28, 1974 RETRIEVABLE BLANKING PLUG [57]ABSTRACT [76] n entor Roy R- van, PO. BOX 38, Artesia, Combinationwireline fishing tool and retrievable N. Mex. 88210 blanking plug foruse in conjunction with a seating nipple. The blanking plug has afishing neck which ex- [22] plied June 1973 tends from a shoulderlocated thereon. The fishing [2l] Appl. No.: 368,717 neck includesspaced overshot engaging members so that a fishing tool in the form ofan overshot can be 52 us. (:1. 166/135, 166/192 engagement members" [51]Int. Cl E2lb 23/00 An axial ee e extending to the blanking p g [58]Field of Search 166/119, 135, 114, 203, a a m ina t p means and pr ssurr li l66/l92 194, 125 means located therein, in the form of spacedbreakable plugs. The counterbore further includes [56] References Citedmeans for releasing the blanking plug from the seating UNITED STATESPATENTS nipple. Attached to the overshot in axially aligned relationshiptherewith is a probe arranged whereby 3 2:2? part of the overshot mustbe positioned in attached 2 905 246 9/1959 Rodger s i... :IIIIIIII: 166114 x relationship between the two Spaced members Order 3:020:958 2/1962Kenneday l66/l 18 for the probe to break a relief P and equalize the3,055,429 9/1962 Tausch 1 1 192 X pressure across the blanking plug.Part of the overshot 3,250,331 5/1966 Boyle 166/135 X must next be movedinto a position between the 3,633,668 l/l972 Vazquez et al. 166/135shoulder and the lowermost overshot engaging member and the secondbreakable plug broken by the Przmary Examiner-David H. Brown probe inorder for the release device to be actuated. Attorney, Agent, orFirmMarcus L. Bates 10 Claims, 9 Drawing Figures WIB 62 I l l. l 61 34ll 1 28 35 l 33 l 1 a? s5 36 l l i l l 64 PATENTEWYZBIW 3812.911

SHE] 2 if 4 Ti FIG. 5

PATENIEI] m 28 m4 sum 3 or 4 FIG. 5

r I l. 'RETRIEVABLE BLANKING PLUG BACKGROUND OF THE INVENTION Seatingnipples for accommodating retrievable blanking plugs take on manydifferent forms and configurations and may be used in a variety oflocations so as to attain any number of different desirable goals. Forexample, seating nipples often are associated with casing packers sothat part of a production string can be located downhole in the boreholeby attachment to the packer. A blanking plug is then placed within thesealing nipple, and the upper part of the production tubing removed froman on/off sealing connection positioned above the packer assembly inorder to enable that portion of the borehole located above the packer tobe subjected to various operations, such as described in my U.S. Pat.No. 3,706,344 issued Dec. 19, I972. At other times, the seating nipplemay be placed elsewhere within a tubing string in order to isolate oneportion of the production string from another.

When the seating nipple is used in conjunction with a tubing stringleading to a high pressure gas formation, great care must be exercisedin removing the retrievable plug from its seating nipple because severalthousand pounds upthrust will propel the plug in a manner similar to aprojectile should the plug be released from its nipple prior toequalizing the pressure thereacross. Should the plug be actuated by awireline fishing tool, the plug, upon being thrust uphole, will becomeentangled in several thousand. feet of wireline or slickline, therebybringing about a very difficult fishing job.

It is possible to equalize the pressure across the packer by theutilization if inert gas pumped into the tubing string. Others haveproposed. a single breakable equalizing plug located within the bridgeplug which can be broken by a wireline actuated tool so as tocommunicate the upper and lower separated lengths of the tubing string;however, when this last expedient is employed, it is still possible forupthrust of the fishing tool to occur. Furthermore, assuming the lastexpedient is successfully carried out,-two costly round trips must bemade into the borehole in order to retrieve the blanking plug.Accordingly, it is desirable to have a combination fishing tool andretrievable bridge plug which can be used in conjunction with theseating nipple and which overcomes all of the above drawbacks, while atthe same time taking advantage of the benefits of the prior art.

SUMMARY OF THE INVENTION This invention comprehends a combinationretrievable blanking plug and fishing tool which enables wire lineretrieval of the plug from a seating nipple when the plug is used toisolate or plug off a portion of the interior of a high pressure tubingstring.

The fishing tool preferably is in the form of an improved overshothaving a cylindrical skirt and an axially aligned longitudinallyextending probe of different diameters. The blanking plug is comprisedof a main body having a shoulder from which there upwardly depends afishing neck having a lifting means in the form of an overshot engagingmember so that the overshot can engage the member. The probe is receivethrough a counterbore which forms an axial passageway extending throughthe fishing neck and through most of the main body of the plug.

Located within the axial passageway are spaced stop means in the fonnofbreakable relief plugs. A release means for actuatinga set of dogs isdisposed above the breakable plugs and include an actuating meanslocated within the axial passageway by which the dogs may be releasedfrom the seating nipple.

The probe has a small inside diameter (id) surface which freely passesthe actuating means of the dogs, and engages and breaks one plug whenthe overshot is captured by the overshot engaging member. A largeoutside diameter (od) portion of the probe engages the release means ofthe dog when the overshot is lowered into further engagement with thelifting means, and after the second breakable plug has been ruptured.

This expeident enables the fishing tool to be latched .onto the fishingneck at all times while removing the blanking or bridge plug, andfurther enables the pres sure differential across the blanking plug tobe safely equalized before the blanking plug is released from theseating nipple. Y

Accordingly, a primary object of the present invention is the provisionof an improved combination of elements which enables a blanking plug tobe removed from a seating nipple in an improved and safe manner, and ina single trip into the borehole.

Another object of the invention is to provide improvements in wirelineactuated blanking plugs which enables the pressure across the plug to beequalized before the plug is released from its seating nipple.

A further object of this invention is to provide both method andapparatus for use in downhole flow restricting apparatus which enables ablanking plug to be removed from the hole by a wireline operated fishingtool in a safe and heretofore unavailable manner.

A still further object of this invention is to provide an improvedcombination retrievable packer and fishing tool which enables the packerto be positioned downhole in a borehole and then retrieved in a singletrip by the novel wireline actuated fishing tool by latching the tooland packer together, relieving the pressure across the packer apparatus,releasing the packer apparatus from the borehole, and then pulling theentire assembly to the surface of the earth by the wireline.

Another object of the invention is the provision of a method ofretrieving a blanking plug from a seating nipple in a single trip by awireline operated fishing tool.

These and various other objects and advantages of the invention willbecome readily apparent to those skilled in the art upon reading thefollowing detailed description and claims and by referring to theaccompanying drawings.

The above objects are attained in accordance with the present inventionby the provision of apparatus fabricated in a manner substantially asdescribed in the above abstract and summary.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a part diagrammatical, partschematical representation of a cross-sectional view of a boreholeformed within the earth, with apparatus made in conjunction with thepresent invention being disclosed therewithin, with some partsbeing-broken away and the remaining parts being shown in cross-sectionsso as to best disclose one operative form of the invention;

FIG. 2 is an enlarged, fragmentary, part crosssectional, sideelevational view of part of the apparatus disclosed in FIG. 1;

FIG. 3 is an enlarged, fragmentary, part crosssectional, sideelevational view of part of the apparatus disclosed in the foregoingfigures;

FIG, 4 is a further enlarged cross-sectional view taken along line 4-4of FIG. 3;

FIG. 5 is a part cross-sectional, enlarged, sideelevational view of afishing tool used in'conjunction with the apparatus of FIGS. 3 and 4;

FIG. 6 is an enlarged, fragmentary, part crosssectional view of part ofthe apparatus disclosed in FIG. 5;

FIGS. 7 and 8 are part cross-sectional illustrations of the operation ofpart of the apparatusdisclosed in the foregoing figures; and

FIG. 9 is a broken, part-cross-sectional view'of a modification of FIG.5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS I FlG. l discloses awell head 10 located at the top of a borehole formed within the groundII, with the borehole being cased at 12 so as to provide access to aproduction formation 13 located downhole in the borehole. Productiontubing 14 provides for flow of hydrocarbons at 15, while a lubricator l6admits wireline 17 into the production tubing in sealed relationshiptherewith, as is known to those skilled inthe art.

The wireline is supportingly attached to a fishing tool I8, which forthe purposes of illustration of this invention'is disclosed as being inthe form of an improved and novel overshot.

Annulus 19 has a conventional packer assembly, schematically illustratedby numeral 20, located therein which maytake on any number of differentforms, as for example a Baker retrievable casing packer product number646-12, described on page 498 of Baker Oil Tool l970-7l catalog, 7400East Slauson Avenue, Los Angeles, California. Located in close proximityof the packer is a seating nipple 21 of conventional design, such asproduct number 801-50 seen on page507 of the before mentioned catalog.The seating nipple screws into the top of the packer, although it can beplaced anywhere in the production tubing string desired. Underlying thepacker is a perforated nipple 22 having perforations 23 therein.

The nipple is flow connected to a sub 24 and affixed to the packer forsupporting a perforating gun 25 such as described in U.S. Pat. No.3,650,640 so that the easing can be perforated as indicated by number26, thereby communicating the interior of the production string with thehydrocarbon bearing formation.

A retrievable blanking plug 27, having a fishing neck 28, has beenplaced within the seating nipple and it is accordingly necessary to beable to remotely remove the plug from the nipple in order to gain accessto the lower portion of the borehole through packer 20. Sub 29 is anon/off sealing connector such as seen on page 499 of the above mentionedcatalog, which enables the upper tubing string to be removed from thepacker assembly should free access to the upper portion of the boreholebe required.

The perforated nipple is provided with a sliding sleeve 30 having portstherein which enables the apertures 23 to be aligned therewith or openedor closed to 4 flow therethrough according to the position of the sleeve30.

As best seen illustrated in FIG. 5, together with certain other figuresof the drawings, the before mentioned fishing tool is disclosed in itssimplest and preferred form as an overshot having a swivel 31 connectedto a reinforced head portion 32 from which there downwardly depends adownwardly opening skirt member 33'. The skirt member is formed of aplurality of lands 34 which are formed by the vertical cutouts 35,thereby forming elongated resilient members which can be outwardlybiased from one another. The lowermost circumferentially disposedterminal edge portion 36 is upwardly turnedat innermost edge portion 37for engagement with the underside of the spaced members located on thefishing neck.

Axially aligned in a concentric manner respective of the skirt and thewireline is a special elongated probe 38 having one end thereof rigidlyaffixed to member 32. The probe reduces in diameter at shoulder 39 toform reduced diameter portion 40 which terminates at the free terminalend 41.

The seating nipple can take on any number of different forms so long asthe inside diameter 42 thereof admits the plug in sealed relationshipthereinto and enables the formation ,of a lock means 43 which, forpurposes of this disclosure, is shown in the form of a circumferentiallyextending concavity having an upwardly directed portion 44.

The main body of the plug is of a constant diameter 45 and hasassociated therewith seal means 46 which are made for sealingly engagingthe inner wall surface of the seating nipple. Any number of designvariations are possible respective to the seal means.

The body includes radially disposed passageways aligned normally to theaxial passageway, and within which there is threadedly affixed spacedbreakable plugs 47 and 48. The plugs have axially aligned counterbores49 formed therewithin, and a free end portion 50 extending into thelower portion of axial counterbore SI. The counterbore forms an axialpassageway of limited length, with the passageway terminating asindicated by the arrow at numeral 52. The bottom of the main body of theretrievable plug is indicated by the numeral 53, while the opposed endof the main body terminates in the form of a circumferentially disposedhorizontal alined annular shoulder 54.

Anchor means in the form of dogs 55,. 56 are pivotally mounted injournaled relationship to the main body by diametrically opposed pinspositioned at 57, so that each of the radially spaced dogs arearticulated within the illustrated body cavity. Opposed cavity walls 58and 59 form a stop means against which the dogs may be abuttinglyreceived. Each dog has an external free end portion which engages thewall surface of groove 43 and further includes a free inner end portion60 which forms a release means located within the axial passageway forcausing the dogs to be moved into a retracted position against wall 58.

The first or uppermost fishing neck member 61 has a contoured uppersurface over which the overshot skirt is guided and a concave lowersurface 62 against which the inside rim of the skirt of the overshot canbe attached in order to lift the plug in an upward direction. Passageway51 extends from end wall 52 through most of the main body and'continuesthrough the fishing neck to where the passageway is outwardly flared at63 for guidably receiving the free end of the probe therewithin.

The second or lower member 64 is made substantially identical to member61 with the second member being spaced from the first member and fromthe shoulder 54 so as to provide lost motion of the overshot along thelongitudinal portions or areas 65 and 66.

In the illustration of FIG. 7, the overshot has been lowered so that theskirt member has been forced to receive the upper lifting membertherewithin. It will be noted that the rim 37 of the skirt is capturedbetween the upper and lower members along the area 65. It will befurther noted that end portion 41 of the reduced diameter portion of theprobe has ruptured the free end portion of the upper stop and reliefplug 47, and is spaced from stop and relief plug 48 with shoulder 39 ofthe-probe being spaced from the release means 60 of the extended dogs.When the overshot is further lowered, the rim or lifting element of theskirt will be brought into close proximity of the upper face of thelower lifting member, with end 41 of the probe resting against the lowerstop member 48.

In FIG. 8 it will be noted that the overshot has been forced to receivethe lower member therewithin, thereby forcing the probe to rupture thelower stop and relief member 48, with the rim of the skirt beingcaptured between the lifting edge of the lower lifting member and theshoulder 54, and with end portion 41 of the probe being slightly spacedfrom bottom wall 52. The large outside diameter portion 38 of the probeis in engagement with the release means at 60 which has caused the dogsto be moved from the illustrated dotted extended position into theillustrated retracted position.

In the embodiment of FIG. 9, overshot 133 has a plurality of lands 134,each of which are provided with a plurality ofupturned edge portions136, 136, 136" for single or plural engagement with one or two liftingmembers 61, 64.

OPERATION In operation, with the blanking plug being used in conjunctionwith the apparatus disclosed in FIG. 1, the plug has already been run tosetting depth and positioned within the seating nipple so as to isolatethe upper and lower portions of the production string from one another,and to enable the upper tubing string to be removed at the on/offsealing connector thereby enabling one to accomplish various desirableoperations on the well. The presence of the plug prevents debris fromfalling into the lower production string below the packer as well asplacing the formation in a shut-in condition. When the upper tubingstring has been replaced and it is desired to remove the plug from theseating nipple, it must be remembered that there is often severalthousand pounds of pressure differential across the plug, andaccordingly, should this pressure fail to be equalized, the plug, whenreleased will be accelerated uphole in the manner of a projectile,thereby entangling the wireline, the overshot. and the plug, whichbrings about a very expensive and complicated fishing job.

Preferably, a mechanical jar 70 and sinker bar is affixed to the uppermember of the overshot by means of sub 71 so that ajarring action can beimparted in either direction into the overshot as may be required. Thetool string of FIG. 1 is run downhole on the wireline,

and as the free end of the probe enters the entrance passageway to thefishing neck, the rim of the overshot will come to rest upon the upperface of member 61. This position gives the wireline operator anindication that the upper member 61 is ready to be received within theovershot. The overshot is next moved down so that it assumes theillustrated position as seen indicated in FIG. 3. Further lowering ofthe overshot brings reduced diameter portion 40 into engagement with thecombination stop and relief means in the form of upper breakable plug47,'with the reduced diameter portion of the probe being freely receivedwithin the free area formed between the spaced release means in theillustrated manner of FIG. 4. The latch formed by the rim or lower skirtportion of the fishing tool can now be reciprocated along length 65 ofthe fishing neck, thereby enabling plug 47 to be broken or sheared. Asimpact causes plug 47 to become broken, the free end 41 of theprobe-moves into engagement with the lower plug, with shoulder 39 of theprobe being spaced above the release means, while the overshot latchmeans rests above lower member 64. If care has been exercised incarrying out this last step, free end portion 41 of the probe will cometo rest upon unsheared plug 48 prior to shoulder 39 engaging the releasemeans of the dog. This action enables the pressure across theretrievable plug to be equalized as gaseous flow occurs along theannulus formed between the outer peripheral surface area of the mainbody of the retrievable plug and the inside peripheral wall surface ofthe seating nipple, through the passageway formed within plug 47 whichnow intercommunicates passageway 51 with the .plug annulus, and frompassageway 51 out of the bugle 63 where flow continues to the well head.

After the pressure has been safely equalized, with the overshot latchedonto the neck, the overshot is jarred down again until the lower plug isruptured, thereby bringing the apparatus into the illustrated positionof FIG. 8 where the overshot can now reciprocate along portion 66 of thefishing neck, all as set forth in the illustrated manner of FIG. 8. Thisexpedient causes shoulder 39 of the probe to engage the release means atof the dogs, thereby retracting the dogs into the illustratedconfiguration seen in FIG. 8. Since the blanking plug is now releasedfrom the seating nipple, the wireline can be used to raise the blankingplug from the well bore, with the rim or latch means formed by theinwardly turned lifting edge 37 of the skirt engaging the concavityprovided on the underside of the lower member of the neck. The bridgeplug is removed from the lubricator of the well in the usual manner, andany subsequent operation can now be carried out on the well bore, as forexample, perforation of the well bore casing, treatment of a lowerformation, or placing the well back onto production, as may be required.

One of the essential teachings of the present invention lies in theproper relative distance 65, 66 respective to the relative distance 36,39, 41 and 60, 47, 48, 52 of the overshot and plug. By making therelative ratios of these various distances an amount according to theteachings of this invention, the above novel practice can be carried outefficiently so as to safely remove a bridging plug or a retrievableblanking plug from a seating nipple or the like. Those skilled in theart, having reviewed this disclosure, will contemplate utilizing anchormeans other than dogs 55, 56 together with the concavity 43. Moreover,it is possible to use seal means 7 on the main body other than theembodiment disclosed at 46. The plug of instant invention can beprovided with dogs which prevent upthrust, downthrust, or a combinationof the two. The practice of the present invention enablesa retrievableplug means to be retrieved from a well bore in a single trip using awireline actuated fishing and release tool. Heretofore, it has beennecessary to make several trips into a borehole in order to equalizepressure and to remove blanking plugs from seating nipples, whereas nowthe plug can be safely removed in a single trip. The novel practice oflatching the fishing tool onto the plug during all of the manipulativeoperations thereof further enhances the desirability of the retrievingoperation. The unexpected advantages of time, labor, safety, andefficiency brought about by the new method and combination, along withthe improved design of the plug and overshot have heretofore beenunavailable in well bore operations using retrievable plugs of the typedisclosed herein.

The use of either embodiment of the overshot disclosed in FIGS. and 8 inconjunction with the bridge plug of the present invention preventsupthrust of the plug upon equalization of the pressure thereacross; andupon release of the plug from its seating nipple, as well as enablingthis sequence of operations to be carried out in a single trip into aborehole. The combination of two spaced relief and stop means in thetool provides a positive surface indication of the below ground actionbeing carried out relative to retrieval of the plug.

The relief plugs should be made of a material which must be broken whenimpacted with several hundred pounds of force imparted by the jar, so asto provide a positive stop means which deliberately must be destroyed orbroken for, the step-wise passage of the probe therethrough. The reliefplugs should be breakable, not bendable, for the reason that a bent plugcould cause malfunction of the tool combination, as will now beunderstood by those skilled in the art.

In using the overshot of HO. 9, only single lifting member 61 need befabricated onto the fishing neck, although two lifting members arepreferred for safety.

I claim: I 1. ln a well bore having a flow conduit located therewithinand a seating nipple located in the flow conduit so that a wirelineoperated fishing tool can retrieve a retrievable blanking plug from theseating nipple, in combination:

said plug having a main body portion for sealingly engaging the insideperipheral wall of the seating nipple, anchor means connected to saidplug and being movable from an extended into a retracted positionrelative to said main body for engagement with the seating nipple; afishingneck means formed on said plug, an axial passageway formedthrough said fishing neck means and into said main body; said fishingneck means having at least one lifting member which can be engaged bysaid fishing tool;

said fishing tool being in the form of an overshot having a downwardlydepending skirt engageable with said lifting member and a probe axiallyaligned with said skirt and slidably received within said axialpassageway; said probe having a large outside diameter portion affixedto said overshot and a small outside diameter free end portion;

release means located in said axial passageway movable by said largeoutside diameter portion of said probe for releasing said anchor meansfrom the seating nipple; spaced upper and lower stop means,

" said upper stop means being a combination stop and pressure equalizingmeans, said spaced stop means being located in said passageway inunderlying relationship respective to said release means in a positionso that said upper stop and pressure equalizing means must be engagedby' said small outside diameter portion of said probe before saidrelease means can be engaged by the large outside diameter portion ofsaid probe;

the relative position of said lifting member, said release means, saidspaced upper and lower stops, the length of said probe, and the relativeposition of said large and small outside diameter portion of said probebeing arranged so that part of the overshot must be engaged with thelifting member in order for the probe to actuate the pressure equalizingmeans, andso that the probe must be positioned below the lowermost stopmeans in order for the large outside diameter of the probe to actuatethe release means.

2. The combination of claim 1 wherein said lower stop means is apressure equalizing means positioned to be actuated by said probe beforethe release means causes the'anchor means to be retracted.

3. The combination of claim 1 wherein said anchor means is a pivotedmember journaled to said main body .and having opposed free ends, onefree end being pivoted away from said body to provide for the anchoraction while the remaining free end is pivoted into the passageway toprovide for the engagement with the probe;

said small outside diameter of said probe passing free of said remainingfree end of said pivoted member while said large outside diameter ofsaid probe engages and moves said remaining free end of said pivotedmember so that said one free end of said pivoted member can be retractedrelative to said main body.

4. The combination of claim 1 wherein said skirt member has anexpandable inwardly directed lower circumferentially extending edgeportion; said lifting member is in the form of an enlargement aboutwhich said skirt member is received when the skirt member is moved in adownward direction, so that the inwardly directed edge portion of theskirt can be latched onto the enlargement, to thereby provide for alifting action respective to said plug.

5. The combination of claim 1 wherein said lower spaced stop means is apressure equalizing means, said upper and lower pressure equalizingmeans being positioned to be contacted and actuated by said probe beforethe release means is retracted;

said skirt member includes an expandable inwardly directed lowercircumferentially extending edge portion; said fishing neck includes asecond lifting member to provide for both an upper and a lower liftingmember, said lifting members being enlargements about which said skirtmember is received in latched relationship respective thereto when theskirt member is moved in a downward direction, so that the inwardlydirected edge portion of the skirt can be latched onto both of theenlargements.

6. In combination, a retrievable blanking plug and a wireline operatedfishing tool for use in a flow conduit located within a borehole;

said retrievable blanking plug having a main body,

means on said main body by which said plug can be placed in sealingengagement with the inside peripheral wall surface of the flow conduit;a lifting member connected to said main bodyfor engagement with saidfishing tool;

anchor means including release means connected to said main body forreleasably engaging the inside peripheral wall of the flow conduit sothat the plug can be anchored therewithin; means forming an obstructedflow passageway through said main body; means on said fishing tool bywhich said obstructed flow passageway is made unobstructed when engagedby the last said means so that the pressure across the plug can beequalized when said fishing tool is placed in a first position ofengagement with said lifting member;

means connected to said fishing tool for causing said anchor means to bedisengaged from the flow conduit when said fishing tool is placed in asecond position of engagement with said lifting member; whereby saidfishing tool can be positioned in said first position of engagementrelative to said plug to enable the pressure across the plug to beequalized, whereupon said fishing tool can then be placed in the secondposition of engagement with said lifting member so that the plug isreleased from engagement with respect to the conduit, thereby enablingthe fishing tool to lift the plug from the flow conduit.

7. The improvement of claim 6 wherein said fishing tool is a wirelineoperated overshot having a skirt member located thereon;

said skirt member has an expandable inwardly directedlowercircumferentially extending edge portion; said lifting member being anenlargement about which said skirt member is received when the skirtmember is telescopingly moved in a downward direction thereover so thatthe inwardly directed edge portion of the skirt can be latched onto theenlargement thereby enabling the fishing tool to lift the plug from theconduit.

8. The improvement of claim 7 wherein said fishing tool has a probethereon and said pressure equalizing means include a combination stopand pressure equalizing means positioned to be contacted by said probebefore the release means is retracted.

9. The improvement of claim 7 wherein said skirt member has anexpandable inwardly directed lower circumferentially extending edgeportion; said lifting member includes upper and lower members in theform of enlargements about which said skirt member is received when theskirt member is moved in a downward direction, so that the inwardlydirected edge portion of the skirt can be latched onto the enlargements.

10. The improvement of claim 7 wherein said fishing tool includes aprobe for providing said releasing means; said pressure equalizing meansinclude a stop means, and further including a lower stop meanspositioned to be contacted by said probe before the release means isretracted;

said lifting member includes an upper and lower enlargement about whichsaid skirt member is received when the skirt member is moved in adownward direction, so that the inwardly directed edge portion of theskirt can be latched onto either of the enlargements.

1. In a well bore having a flow conduit located therewithin and aseating nipple located in the flow conduit so that a wireline operatedfishing tool can retrieve a retrievable blanking plug from the seatingnipple, in combination: said plug having a main body portion forsealingly engaging the inside peripheral wall of the seating nipple,anchor means connected to said plug and being movable from an extendedinto a retracted position relative to said main body for engagement withthe seating nipple; a fishing neck means formed on said plug, an axialpassageway formed through said fishing neck means and into said mainbody; said fishing neck means having at least one lifting member whichcan be engaged by said fishing tool; said fishing tool being in the formof an overshot having a downwardly depending skirt engageable with saidlifting member and a probe axially aligned with said skirt and slidablyreceived within said axial passageway; said probe having a large outsidediameter portion affixed to said overshot and a small outside diameterfree end portion; release means located in said axial passageway movableby said large outside diameter portion of said probe for releasing saidanchor means from the seating nipple; spaced upper and lower stop means,said upper stop means being a combination stop and pressure equalizingmeans, said spaced stop means being located in said passageway inunderlying relationship respective to said release means in a positionso that said upper stop and pressure equalizing means must be engaged bysaid small outside diameter portion of said probe before said releasemeans can be engaged by the large outside diameter portion of saidprobe; the relative position of said lifting member, said release means,said spaced upper and lower stops, the length of said probe, and therelative position of said large and small outside diameter portion ofsaid probe being arranged so that part of the overshot must be engagedwith the lifting member in order for the probe to actuate the pressureequalizing means, and so that the probe must be positioned below thelowermost stop means in order for the large outside diameter of theprobe to actuate the release means.
 2. The combination of claim 1wherein said lower stop means is a pressure equalizing means positionedto be actuated by said probe before the release means causes the anchormeans to be retracted.
 3. The combination of claim 1 wherein said anchormeans is a pivoted member journaled to said main body and having opposedfree ends, one free end being pivoted away from said body to provide forthe anchor action while the remaining free end is pivoted into thepassageway to provide for the engagement with the probe; said smalloutside diameter of said probe passing free of said remaining free endof said pivoted member while said large outside diameter of said probeengages and moves said remaining free end of said pivoted member so thatsaid one free end of said pivoted member can be retracted relative tosaid main body.
 4. The combination of claim 1 wherein said skirt memberhas an expandable inwardly directed lower circumferentially extendingedge portion; said lifting member is in the form of an enlargement aboutwhich said skirt member is received when the skirt member is moved in adownward direction, so that the inwardly directed edge portion of theskirt can be latched onto the enlargement, to thereby provide for alifting action respective to said plug.
 5. The combination of claim 1wherein said lower spaced stop means is a pressure equalizing means,said upper and lower pressure equalizing means being positioned to becontacted and actuated by said probe before the release means isretracted; said skirt member includes an expandable inwardly directedlower circumferentially extending edge portion; said fishing neckincludes a second lifting member to provide for both an upper And alower lifting member, said lifting members being enlargements aboutwhich said skirt member is received in latched relationship respectivethereto when the skirt member is moved in a downward direction, so thatthe inwardly directed edge portion of the skirt can be latched onto bothof the enlargements.
 6. In combination, a retrievable blanking plug anda wireline operated fishing tool for use in a flow conduit locatedwithin a borehole; said retrievable blanking plug having a main body,means on said main body by which said plug can be placed in sealingengagement with the inside peripheral wall surface of the flow conduit;a lifting member connected to said main body for engagement with saidfishing tool; anchor means including release means connected to saidmain body for releasably engaging the inside peripheral wall of the flowconduit so that the plug can be anchored therewithin; means forming anobstructed flow passageway through said main body; means on said fishingtool by which said obstructed flow passageway is made unobstructed whenengaged by the last said means so that the pressure across the plug canbe equalized when said fishing tool is placed in a first position ofengagement with said lifting member; means connected to said fishingtool for causing said anchor means to be disengaged from the flowconduit when said fishing tool is placed in a second position ofengagement with said lifting member; whereby said fishing tool can bepositioned in said first position of engagement relative to said plug toenable the pressure across the plug to be equalized, whereupon saidfishing tool can then be placed in the second position of engagementwith said lifting member so that the plug is released from engagementwith respect to the conduit, thereby enabling the fishing tool to liftthe plug from the flow conduit.
 7. The improvement of claim 6 whereinsaid fishing tool is a wireline operated overshot having a skirt memberlocated thereon; said skirt member has an expandable inwardly directedlower circumferentially extending edge portion; said lifting memberbeing an enlargement about which said skirt member is received when theskirt member is telescopingly moved in a downward direction thereover sothat the inwardly directed edge portion of the skirt can be latched ontothe enlargement thereby enabling the fishing tool to lift the plug fromthe conduit.
 8. The improvement of claim 7 wherein said fishing tool hasa probe thereon and said pressure equalizing means include a combinationstop and pressure equalizing means positioned to be contacted by saidprobe before the release means is retracted.
 9. The improvement of claim7 wherein said skirt member has an expandable inwardly directed lowercircumferentially extending edge portion; said lifting member includesupper and lower members in the form of enlargements about which saidskirt member is received when the skirt member is moved in a downwarddirection, so that the inwardly directed edge portion of the skirt canbe latched onto the enlargements.
 10. The improvement of claim 7 whereinsaid fishing tool includes a probe for providing said releasing means;said pressure equalizing means include a stop means, and furtherincluding a lower stop means positioned to be contacted by said probebefore the release means is retracted; said lifting member includes anupper and lower enlargement about which said skirt member is receivedwhen the skirt member is moved in a downward direction, so that theinwardly directed edge portion of the skirt can be latched onto eitherof the enlargements.